Respiratory monitors and ventilators are known in the art. Typically, ventilators make noises because of pneumatic pressures and flows, and because of the mechanical devices involved. In a traditional operating room, there are various visual alarms that are used as indicia of a patient respiratory rate and depth. Clinicians giving anesthesia are required to monitor the various gauges, displays and screens on an anesthesia machine and the ventilator continuously to ensure that the patient is receiving proper care.
However, these clinicians are busy doing many things during an operation and cannot look at the video monitors, screens, etc. constantly for information on the patient's ventilatory status. Accordingly, it would be advantageous for the clinician to be able to continuously monitor the patient's respiratory characteristics without diverting the clinician's attention from other tasks.
Several patents have tried to solve this problem. U.S. Pat. No. 5,970,973, issued to Gonda et al., discloses a method for delivering insulin lispro. The need for delivering insulin by injection can be reduced by a method whereby an aerolyzed insulin formation is delivered to a patient's lungs. The Gonda et al. patent discloses that in order to carry out an inhale-exhale maneuver of the invention, it is preferable to use a sensor that can signal the patient that a maximal inhale maneuver and a maximal exhale maneuver have been correctly accomplished. The device can issue a common sound when the device has sensed that a maximal inhale maneuver or a maximal exhale maneuver has been accomplished, or the device can flash a green light. The Gonda et al. patent is directed to delivering a sufficient amount of insulin into the bloodstream through inhalation and may require the patient to use a maximum level of both inhalation and exhalation volume.
U.S. Pat. No. 5,836,302, issued to Hometh et al., discloses an audible wave form system for sensing pressure in the patient's airway and emitting an audible wave form based on that pressure. In particular, the system provides a short duration sound in the form of bursts when the pressure of the airway changes by a predetermined incremental amount. A pressure transducer monitors the pressure in the breathing circuit for both inhalation and exhalation, and outputs an audio wave form whenever a certain change in pressure is detected. The frequency of the audible bursts are proportional to the airway pressure so that a particular audible burst will be at the same frequency at the same pressure whether in the inhalation cycle or the exhalation cycle.
U.S. Pat. No. 4,602,644, issued to DiBenedetto et al., discloses a device using a sensor/signal processor that monitors respiration pressure waves and generates corresponding acoustic signals therefrom in a more preferred frequency band. The sensor processor distinguishes between inhalation and exhalation, analyzes the respiration characteristic and uses a pair of thresholds in combination with time monitoring to ensure that inhalation occurred and establish the expected occurrence of exhalation.
U.S. Pat. No. 4,576,178, issued to Johnson, discloses an audio signal generator that can monitor a psychological condition and provide a corresponding audio output signal that varies in correspondence with the monitored psychological condition. U.S. Pat. No. 4,366,821, issued to Wittmaier et al., discloses a breath monitoring device that uses a threshold circuit to differentiate between inhalation and exhalation and which uses a buzzer that emits a common audible sound for failure to meet threshold rates during inhalation and exhalation.
U.S. Pat. No. 3,867,934, issued to Oliver, discloses a pressure monitor that uses high and low limit detectors for monitoring a patient's airway pressures. U.S. Pat. No. 5,730,140, issued to Fitch, discloses a device that utilizes synthesized realistic body sounds that are emitted in accordance with monitored psychological parameters. Moreover, U.S. Pat. No. 5,738,106, issued to Yamamori et al., discloses a device that detects a signal that time varies in accordance with CO2 concentration and a respiration gas, and utilizes a beeper that emits a respective sound depending on the change in CO2 concentration.
However, the prior art does not provide a ventilation sound detection system that emits distinctive sounds for a proper inhalation by a patient and a proper exhalation by the patient by continuously monitoring the patient's inhalation and exhalation. Such a system is needed to impart significant information about the breath delivered and received by the ventilator.